Re: self-paging

[Bas Wijnen]

On Wed, Nov 30, 2005 at 07:00:40PM +0100, Bas Wijnen wrote:
> No, I don't think this is quite correct.  You are right that the actual paging
> out of memory to disk is still done by "the system", not by the application.
> So strictly speaking it may not be self paging.  But it is much stronger than
> advisory.  The system is not allowed to swap out pages in a different order
> than the process indicates.  This is why I call it self-paging: because the
> paging decisions ("which page will be swapped out next?") are made locally.
> 
> The other type of paging decisions ("which process will have a page swapped
> out _right now_?") is indeed not made by the process.  However, if it is, I
> don't see how a denial of service can be prevented when a process decides not
> to cooperate.  As discussed before, the problem is that it is not possible to
> see if a task is not cooperating or just slow.
> 
> So I think this is the closest we can get to self paging without opening the
> system to attacks.

And what I forgot to say: In the stable situation, where the quota aren't
changing, a process does directly swap out a page when it moves it in the
list.  So if the rest of the system doesn't do anything, the process really
pages itself (via a system call to the global pager, but that one really does
just what is expected of it).  If the system does do something, then the
process doesn't define how many pages it has (except if it stays below its
quota), but that is a Good Thing(tm).

Thanks,
Bas

-- 
I encourage people to send encrypted e-mail (see http://www.gnupg.org).
If you have problems reading my e-mail, use a better reader.
Please send the central message of e-mails as plain text
   in the message body, not as HTML and definitely not as MS Word.
Please do not use the MS Word format for attachments either.
For more information, see http://129.125.47.90/e-mail.html

signature.asc
Description: Digital signature